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Saturday, May 17, 2014

No, That WASN'T A Surprise Tornado In Vermont Early Saturday Morning. Was Microburst

6:30 p.m. SATURDAY UPDATE:
National Weather Service meteorologists from South Burlington hightailed it to Craftsbury this afternoon to check out whether some wind damage was due to a tornado.

James Sinko took this photo of a pole impaled into a
metal roof in Craftsbury, Vermont after an early
Saturday microburst. Photo via @JamesSinko on Twitter.

The area had been under a tornado warning early Saturday morning after meteorologists detected rotation in the clouds above.

Even though nobody wants to see property damage, a microburst sounds vaguely disappointing, compared to a tornado.

However, microbursts are often as dangerous as a tornado.

Just check out the damage, as inventoried by the National Weather Service inspection of the damage in Craftsbury, near the intersection of Collinsville and Wild Branch roads.

A roof was torn off a barn, several trees fell over, there was minor damage to a home, and a pole was impaled into the roof of a shed.

A turkey hunter nearby who was out when the microburst hit said he heard the sound of a tornado. That's not surprising. A microburst, a rushing gush of wind, can sound like a twister.

A microburst is an outflow of violent wind from a severe thunderstorm. They cover areas of less than 2.5 miles wide and almost never last more than five minutes.

Meteorologists who inspect damage like what happened in Craftsbury can often readily tell whether the mess was caused by a microburst or a tornado. A microburst knocks down trees and scatters debris pretty much in just one direction. A tornado will topple trees in a variety of directions, and debris will fly every which way.

The National Weather Service conclusion that the storm was a microburst rather than a tornado is preliminary. They'll analyze things a bit more before putting this investigation to bed.12:30 p.m. SATURDAY UPDATE

As you can see by the reader comment at the bottom of this post, there are reports of wind damage near Wolcott and Craftsbury last night. That's right in the area that the National Weather Service in South Burlington issued a tornado warning.

A meteorologist at the South Burlington National Weather Service office just told me they are sending people up that way this afternoon to see if there is evidence of wind damage, and whether that damage was caused by a tornado or straight line winds.

The meteorologist said radar indicated rotation aloft. However, Doppler radar, based in Colchester, Vermont, has a hard time seeing down near the surface, because mountains block the view. Radar first detected rotation more to the south, near Worcester or that area, then it moved north to Wolcott.

The mountains block the view of the radar toward Wolcott even more than they do more to the south, so it was surely hard for the National Weather Service to determine whether there was indeed some sort of tornado going on.

It looks to me out of an abundance of caution, given the rotation aloft, that they issued the pre-dawn tornado warning.

The assessment team should be back later this afternoon and the National Weather Service will put out a statement later today on whether they think a tornado touched down, or whether any damage was caused by straight line winds.PREVIOUS DISCUSSION FOLLOWS:

I slept in late this rainy Saturday morning and was shocked into full wakefulness when I discovered there was a tornado warning for central Vermont, just 20 or 30 miles to my east early this morning.

A tornado ripped the roof of of an apartment building
in Washington, Vermont in May, 2009.

The tornado warnings came around 4 a.m., especially around the towns of Worcester, and later Wolcott, as the National Weather Service in South Burlington detected rotation in a line of storms that was making its way through the state.

As of 8 a.m. Saturday, the National Weather Service tells me there are no reports of touchdowns and no reports of damage.

My guess is there was indeed rotation on radar, but the swirling did not reach the ground.

Or, since that section of Vermont is pretty remote, a tornado maybe touched down in a place where there are no people and no structures.

It's still dark at 4 a.m., so nobody would have seen a twister. Plus, if there was one, it was probably rain wrapped, as there was a lot of heavy rain involved.

Still, that there was enough rotation in the storms to warrant a tornado warning comes as a big surprise to me.

First of all, tornadoes are usually the product of supercell thunderstorms, which typically reach their peak intensity in the late afternoon or evening, not just before dawn.

But sometimes, in a weather pattern like this, with storms moving north fast, within a slowly moving line of rain, you get rotation and spin up thunderstorms.

The project lists 68 additional injuries from Vermont tornadoes, but those 68 injuries were from a tornado that crossed from New York State into Bennington County, Vermont on May 31, 1998. All the injuries associated with that tornado occured in New York State.

That tornado was the only EF3 intensity twister on record in Vermont since 1953. The rest have been between EF0 and EF2. That means, except for the 1998 tornado, all twisters had winds of 135 mph or less. Most of the tornadoes were EF0, meaning they had winds of between 65 and 85 mph.

If there is a tornado alley in Vermont, the Tornado History Project suggests two of them: One in Franklin County, in far northwestern Vermont, and the other in far southern Vermont. According to the history's map, those two locations have the heaviest concentrations of tornado touchdowns, and virtually all of the EF2 intensity twisters.

If there is any new information on whether there was a tornado in central Vermont last night, I'll update this post.

5 comments:

I felt the tornado go by while turkey hunting in Craftsbury this morning. There was lightning, strong winds, and heavy rain. It damaged my friend's farm pretty badly, just west of Craftsbury Common on the North Wolcott Road.

Yikes! We are in Montpelier just northeast of the town center up the hill... When that storm passed through there was a heavy enough downpour to wake me up but no winds of note (not even twigs blown down) and no thunder either. Pretty remarkable that just a bit to the north it might have dropped a tornado.

It would be awesome if there were better radar coverage of this side of the Greens, but I guess it's probably low priority to build a weather radar here.

Charlie: Your comments on more radar ar true, but radar on your side of the mountain would have trouble w/mountains, too. NWS in Burlington says storms had little if any lightning, which explains why you heard no thunder. I'm told if there is wind damage, it's VERY localized.

I've had two microbursts (I'm about 15 mi. sw of Middlebury) in the last 8 years-- roughly 5 minutes of really, really wild, briefly actually very scary wind and rain in the middle of fairly ordinarily heavy rain/wind storms. I went through two Cat 1 hurricanes in another state, and these bursts were fully as violent. Both took down large and small trees and large limbs only in a fairly small area, damage about 1/4 mile from me in one direction, but not the other, and no visible damage anywhere else in the area. Both were in late afternoon, and both were so thoroughly "rain-wrapped," I wouldn't have been able to see a funnel if there had been one.

But my events match perfectly to your description of the difference between a microburst and a tornado.

(btw, Matt, there's a critical typo in your post above-- "A tornado knocks down trees and scatters debris pretty much in just one direction. A tornado will topple trees in a variety of directions, and debris will fly every which way."

Oh, my god, Matt, do you have any idea the hoops we have to jump through to be able to leave you a comment? I tried option after option and finally ended up registering with AIM, which renders my username as the gobbledygook above.

Any chance your system will at least let you add Disqus, which is becoming very widely used across many blogs? There are a lot of us out here who don't use gmail or yahoo or Facebook or aol.